1. Field of the Invention
This invention relates to the novel thermosetting imide oligomer. More specifically, it relates to an imide oligomer which is able to provide a polyimide having excellent heat resistance, hygroscopic resistance, electric properties, and suitable reactivity for laminating and moulding purposes, and it also relates to a manufacturing method of a heat resistant laminated sheet having superior heat resistance, hygroscopic resistance and electric properties.
2. Description of the Prior Art
The thermosetting resins are usually used for various fields such as insulating materials and structural materials as materials for injection, impregnation, lamination and moulding. Recently, the restrictions on the use of these materials in various usages have become stricter and, particularly, the heat resistance of materials has become highly important. Conventionally, thermosetting polyimide resins and heat resistant epoxy resins have been used where the heat resistance is required.
Among these materials, there are known many thermosetting polyimide resins but "Kerimide(.TM.)" is often used which principally consists of a combination of a bismaleimide compound and diaminodiphenylmethane.
Recently, a both end-terminated thermosetting polyimide which uses 3-aminophenylacetylene as an amine for end-termination is on the market as "Thermid(.TM.)" (Hughs Air-craft, Japanese non-examined publication No. 50-5348 etc.). Although several methods are known about the synthesis of the above mentioned 3-aminophenylacetylene (for example, U.S. Pat. No. 4,125,563), there are problems that all these synthetic routes are too long and also the reagents used are expensive.
Also proposed is a both end-terminated thermosetting polyimide which uses propargyl amine as an amine for endtermination (Ube Kosan Co., Ltd. Japanese non-examined publication Nos. 2-284923, 3-174427).
In another aspect, the development of electronic equipment is remarkable and a copper laminated board used as a printed wiring board is required to have superior properties and a wider variety of usages. Particularly, as the wiring has become highly densitive due to further development of high density mounting of electronic parts, the multiplication of layers and minimization of through holes in wiring board is progressing. Consequently, good processing properties are required for the copper laminated board such as less smear occurrence in the drilling operation.
Besides the improvement in productivity and requirement of cost reduction, the processing conditions require much more strict attention in the assembling process of wiring boards, such as hot air leveler and reflow soldering. According to these requirements, much higher heat resistance and hygroscopic resistance are demanded for the copper laminated board as the substrate.
In order to satisfy these requirements, an addition curing type polyimide resin is recently utilized instead of an epoxy resin which was widely used as a laminated sheet material for the copper laminated board. Using this polyimide resin as a laminated sheet material for the copper laminated board, the remarkable advantages can be seen in that the smear in drilling operation hardly occurs and the heat resistance for processing operation and in long term tests are improved.
However, an addition curing type polyimide resin which was used in the past has the following problems. The material made by the reaction between bismaleimide and diaminodiphenylmethane is superior in use of laminated sheets, however, on the contrary, it has a problem of short time allowability for varnish and prepreg due to the high reactivity with diaminodiphenylmethane. In addition, the human toxicity of diaminodiphenylmethane is also in question. Also, there is a problem of inferior hygroscopic resistance resulting from diaminodiphenylmethane used as a curing agent and a special caution to the humidity during the long term storage is required.
The propargyl group disclosed by the Japanese non examined publication No. 2-284923 has a high thermal reaction starting temperature of 250.degree. C., and it is known that an imide oligomer which uses the propargyl group as a reacting group is inferior in moulding properties due to the high thermosetting temperature. Moreover, it is pointed out that the polyimide resin is also generally inferior in hygroscopic resistance and may cause some trouble in the dimensional stability at the moulding process.